Reefluvr,i use the same gravity fed system your gonna be doing.The best way to do it is use the same type of connectors that your RO/DI uses.(the kind you just push in,forget the name)You can get them at HD,get the one with a shut-off valve with one connection for your RO tubing to float valve.The other end of the connector i believe is threaded .5" You just drill a .5" hole(slightly smaller in your top-off container/bucket about 1-2 " from bottom of bucket).The connector will thread itself into the hole in the bucket.Use sealant when threading it through.Then just push one end of the tubing into the end of the valve/connector and the other end to your float valve.You will be glad you went with the valve type(RO style)connector because it will allow you to shut off the flow when your mixing kalk and allowing it to settle before opening it back up to feed your float-vavle.If you need a pic,LMK